Prostaglandins are a group of long-chain, unsaturated hydroxy and hydroxyketocarboxylic acids comprising a cyclopentane ring. From the chemical point of view, prostaglandins are derivatives of prostan-acid, which has the following structure: ##STR3## There exists a series of prostaglandins occuring in nature. The prostaglandin PGE.sub.1, for example, has the following structure ##STR4## while prostaglandin PGF.sub.1 corresponds to the following structure ##STR5## and prostaglandin PGA.sub.1 corresponds to the following structure ##STR6##
Prostaglandins occur in the tissue of many mammals in different quantitative ratios and a corresponding variety can be observed also in regard to the physiological properties of this class of compounds. There is known to be a series of quite important pharmacological effects associated with separate prostaglandins. In addition to influencing the heart frequency and lowering the blood pressure, prostaglandins also prevent the adhesion and aggregation of platelets, which represent the first step to thrombosis.
However, in spite of such quite valuable spectrum of effects, prostaglandins could hardly be used for pharmacological purposes until the present time, since their half-value life in blood amounts to only about 10 minutes. Accordingly, in the past there has been no lack of experiments in attempting to eliminate this deficiency through the provision of suitable derivatives of prostaglandin. Thus, the U.S. Pat. Nos. 3,632,627 and 3,746,728 describe processes of esterifying prostaglandins with glycerin or esters of glycerophosphoric acid, in which connection one obtains ester compounds corresponding to the formula ##STR7## wherein one of the radicals R.sub.1, R.sub.2, R.sub.3 is a prostaglandin group, the other radicals being, as the case may be, hydrogen or radicals of stearic acid, palmitic acid or phosphoric acid having the formula ##STR8## wherein R.sub.4 is hydrogen or the ##STR9## radical, while R.sub.5 can be one of the groups: ##STR10##
The physiological effectiveness of these compounds, i.e., the duration of effect of the prostaglandins, should be extended through the formation of derivatives.